This is a question that none of us will know if it is required as you will have to get your water tested first. If the Cation load in you water is very high then yes you will see the benefits of adding an water softner which is Cation based. This will then reduce the load on your R/O.
On the opposite side if your Cation load in you water is very low then will not have much impact. It's a try and see situation, some see benefits some don't due to low Cation load in their water.